1. Technical Field
The present invention relates to a lead forming apparatus and a method of fabricating a semiconductor device.
2. Related Art
In a method of manufacturing a semiconductor device having a plurality of outer leads in the outer periphery of a molding resin encapsulating a semiconductor chip, the semiconductor chip is placed on a lead frame and then encapsulated with a resin, the product is then subjected to processes including flash removal of the molding resin, solder plating and so forth, and finally subjected to finishing of leads (referred to as “lead forming”, hereinafter).
The lead forming process of semiconductor device includes cutting leads to separate a semiconductor device from a lead frame, bending leads (outer leads) into a predetermined geometry, and cutting the ends of leads so as to adjust them to a specified dimension. As for semiconductor devices of the surface mounting type, the leads are formed into a gull wing shape characterized by horizontal projection, followed by downward bending, and again by horizontal bending, and so as to have a predetermined dimension of leads.
A technique of carrying out these procedures of lead forming in a single step has recently been developed.
Japanese Laid-Open Patent Publication No. 2001-168257 describes a die capable of bending, and then cutting, the outer leads of a lead frame in a single stroke. Japanese Laid-Open Patent Publication No. H8-23060 describes a method of cutting leads by which the ends of leads are cut while adjusting them to a predetermined length, and the leads are then bent in a Z-form, characterized in that the leads are cut just as being torn off by a pressing force of a lead forming punch struck thereon, and that the leads are bent by completely pressing them to a bending component.
Japanese Laid-Open Patent Publication No. H2-87561 describes a die capable of forming leads of a semiconductor device placed on a forming die, which is used as a lower die, by pressurizing them with a forming punch, which is used as an upper die.
Holding of the leads with the dies in the process of lead bending may, however, cause scratches or peeling of solder plating of the leads, and this may cause abnormal appearance of the semiconductor device, may cause contact failure in the process of mounting of the semiconductor device, may degrade quality of the semiconductor device due to adhesion of fallen debris onto the surface of the leads, may cause abnormal appearance of the semiconductor device or degradation in strength of the leads, due to residence or deposition of fallen debris in the dies, and consequent excessive pressure locally exerted when the leads are held.
Japanese Laid-Open Patent Publication No. H8-102513 describes a configuration of the die shaped so as to scarcely contact with the work to be processed in the portion thereof not subjected to bending, and having, at the upper portion thereof, a deposition guiding surface composed of a curved surface continued from the bending surface, and a hole discharging deposits therethrough. The configuration is reportedly capable of largely reducing production of the debris of plating, and of thereby preventing failures such as inter-lead short circuiting.
These conventional techniques have, however, been suffering from the problems below:
(1) the leads are formed into the same geometry with the dies, because the leads in the process of bending are clamped between the dies, without a function of adjusting geometry and dimension of the leads; and
(2) the dies are necessarily formed in the same geometry with the leads because the leads in the process of bending are held between the dies, thereby the die components may require complicated and precision machining, period of manufacture and delivery thereof may become longer, and cost for the manufacture may increase.